It is well known in the electronic computer art that a computer system includes at least one printed circuit board having printed circuitry, signal planes, voltage planes, ground planes and plated through holes. The board is electrically connected to the computer by distribution cables which transmit input-output signal information. In many applications, a plurality of printed circuit cards are connected to the board. These cards contain printed circuitry and electronic components and serve as the heart and brain of a computer system. Each card has on both sides along one edge one or more rows of circuit tabs and may, if desired, have a similar arrangement of tabs along the opposite edge. Various types of edge connectors may be used to connect the cards to the circuit board. A preferred type of connector is a zero insertion force connector which permits easy insertion and removal of a card with no resulting damage and contacts the card tabs with a wiping action to make a good electrical contact. The connector plugs into the plated through holes in the circuit board and has opposing rows of flexible spring contacts which are cammed into an open position or a closed position. When cammed to the open position, the circuit card may be inserted or removed in either a horizontal or vertical direction. When the card is inserted, the spring contacts are cammed to the closed position and will engage the card tabs with a vertical wiping action.
However, it was found that sometimes the force of the wiping action of the spring contacts will cause the card to move, resulting in contact misregistration and loss of wiping. Also, if the card is inserted improperly, the contact fingers will not contact the right card tabs, resulting in electrical shorts, etc. It became evident that retention means and polarization means were needed to prevent the card from moving and to insure that it is inserted correctly.